Method and apparatus for controlling light bandwidth

ABSTRACT

An apparatus includes a light source that produces a light beam, a bandwidth measurement system, a plurality of bandwidth actuation systems, and a control system. Each bandwidth actuation system includes one or more bandwidth actuators and each bandwidth actuation system is connected to an optical feature that is optically coupled to the produced light beam and operable to modify the connected optical feature to select a bandwidth within a bandwidth range of the produced light beam. The control system is connected to the bandwidth measurement system and to the plurality of bandwidth actuation systems. The control system is configured to switch between activating and operating a first bandwidth actuation system and activating and operating a second bandwidth actuation system independently and separately of activating and operating the first bandwidth actuation system based on a provided bandwidth measurement and a selected target bandwidth.

TECHNICAL FIELD

The disclosed subject matter relates to a method for controlling laserlight bandwidth.

BACKGROUND

An accurate knowledge of a bandwidth of an optical source such as alaser is important in many scientific and industrial applications, suchas, for example, for critical dimension control in deep ultraviolet(DUV) semiconductor photolithography in which a substrate or wafer isirradiated by a light beam produced by the optical source while thesubstrate or wafer is moved axially along an optical axis of the lightbeam.

The bandwidth of laser light is the width of the intensity spectrum ofthe laser light output from the laser, and this width can be given interms of wavelength or frequency of the laser light. Any suitable metricor mathematical construction related to the details of the opticalsource spectrum can be used to estimate the bandwidth of the laserlight. For example, the full width of the spectrum at a fraction (X) ofthe maximum peak intensity (referred to as FWXM) can be used to estimatethe laser light bandwidth. As another example, a width of the spectrumthat contains a fraction (Y) of the integrated spectral intensity(referred to as EY) can be used to estimate the laser light bandwidth.

SUMMARY

In one general aspect, a method includes producing a light beam;enabling control of a bandwidth of the produced light beam within afirst range of bandwidths including enabling the activation and controlof a first bandwidth actuation system connected to a first opticalfeature optically coupled to the produced light beam; and enablingcontrol of a bandwidth of the produced light beam within a second rangeof bandwidths including enabling the activation and control of a secondbandwidth actuation system connected to a second optical featureoptically coupled to the produced light beam. The second range ofbandwidths is distinct from the first range of bandwidths.

Implementations can include one or more of the following features. Forexample, the method can also include receiving a request to change abandwidth of the produced light beam from the first range of bandwidthsto the second range of bandwidths. The method can include switchingbetween bandwidth control within the first range and bandwidth controlwithin the second range in response to a command to switch.

The method can include switching between bandwidth control within thefirst range to bandwidth control within the second range. The switchingincludes selecting second target bandwidth information; setting thefirst bandwidth actuation system to a first fixed state; switching abandwidth measurement system from a first configuration to a secondconfiguration; receiving measured bandwidth information from thebandwidth measurement system while operating in the secondconfiguration; determining whether the measured bandwidth informationmatches the second target bandwidth information; and activating thesecond bandwidth actuation system to cause the second optical feature tomodify the bandwidth of the produced light beam until it is determinedthat the measured bandwidth information matches the second targetbandwidth information. The method can include storing information aboutthe state of one or more components of the first bandwidth actuationsystem before setting the first bandwidth actuation system to the firstfixed state.

The first fixed state can be the state of the first bandwidth actuationsystem at the moment the request to change the bandwidth of the producedlight beam from the first bandwidth range to the second bandwidth rangeis received. The first fixed state can be determined from a function ofthe state of the first bandwidth actuation system at the moment that arequest is received to change the bandwidth of the produced light beamfrom the first bandwidth range to the second bandwidth range.

The method can include controlling the second bandwidth actuation systemto reduce an absolute error between the measured bandwidth informationand the second target bandwidth information until a request is receivedto change the bandwidth of the produced light beam from the secondbandwidth range to the first bandwidth range.

The method can include controlling the second bandwidth actuation systemin a reset mode after switching the bandwidth measurement system fromthe first configuration to the second configuration.

The method can include switching between bandwidth control within thesecond range to bandwidth control within the first range upon receipt ofthe request to change bandwidth of the produced light beam from thesecond bandwidth range to the first bandwidth range. The switchingincludes selecting first target bandwidth information; setting thesecond bandwidth actuation system to a second fixed state; switching thebandwidth measurement system from the second configuration to the firstconfiguration; receiving measured bandwidth information from thebandwidth measurement system while operating in the first configuration;determining whether the measured bandwidth information matches the firsttarget bandwidth information; and activating the first bandwidthactuation system to cause the first optical feature to modify thebandwidth of the produced light beam until it is determined that themeasured bandwidth information matches the first target bandwidthinformation.

The second fixed state can be the state of the second bandwidthactuation system at the moment the request to change the bandwidth ofthe produced light beam from the second bandwidth range to the firstbandwidth range is received. The second fixed state can be apre-determined state that is determined during calibration.

The method can also include controlling the first bandwidth actuationsystem to reduce the absolute error between the measured bandwidthinformation and the first target bandwidth information until a requestis received to change the bandwidth of the produced light beam from thefirst bandwidth range to the second bandwidth range. The method can alsoinclude sending a signal to the first bandwidth actuation system toreturn to the state that was stored prior to setting the first bandwidthactuation system to the first fixed state. The method can also includecontrolling the first bandwidth actuation system in a reset mode afterswitching the bandwidth measurement system from the second configurationto the first configuration.

The method can include switching between bandwidth control within thefirst range to bandwidth control within the second range. Switchingbetween bandwidth control within the first range to bandwidth controlwithin the second range can include switching a bandwidth measurementsystem from a first configuration to a second configuration.

Switching the bandwidth measurement system from the first configurationto the second configuration can include switching from a first set ofcalibration variables to a second set of calibration variables. Thefirst set of calibration variables can be predetermined and configuredto provide a metric that is tuned to estimate bandwidth over the firstrange of bandwidths; and the second set of calibration variables can bepredetermined and configured to provide a metric that is tuned toestimate bandwidth over the second range of bandwidths.

The light beam can be produced by producing a laser beam.

In another general aspect, an apparatus includes a light source thatproduces a light beam; a bandwidth measurement system configured toreceive a portion of light beam output from the light source andconfigured to measure a bandwidth of the light beam portion and toprovide the bandwidth measurement; a plurality of bandwidth actuationsystems, each bandwidth actuation system including one or more bandwidthactuators and each bandwidth actuation system being connected to anoptical feature that is optically coupled to the produced light beam andoperable to modify the connected optical feature to select a bandwidthwithin a bandwidth range of the produced light beam; and a controlsystem connected to the bandwidth measurement system and to theplurality of bandwidth actuation systems. The control system isconfigured to switch between activating and operating a first bandwidthactuation system and activating and operating a second bandwidthactuation system independently and separately of activating andoperating the first bandwidth actuation system based on a providedbandwidth measurement and a selected target bandwidth.

Implementations can include one or more of the following features. Forexample, the apparatus can also include a target bandwidth switch thatis configured to be set at a target bandwidth that is within a targetbandwidth range selected from a plurality of distinct target bandwidthranges. The apparatus can include a lithography apparatus that receivesthe produced light beam.

The light source can include a laser source and the light beam can be alaser beam.

At least one of the optical features can include a dispersive element.At least one of the optical features can include a beam expander.

In another general aspect, a method of controlling a bandwidth of apulsed laser beam includes producing the pulsed laser beam; receivingmeasured bandwidth information of the produced laser beam from abandwidth measurement system; and based on the received measuredbandwidth information, controlling a bandwidth of the produced laserbeam to within a plurality of ranges of bandwidths including activatingand controlling a plurality of bandwidth actuation systems eachconnected to an optical feature optically coupled to the produced laserbeam. Each range of bandwidths in the plurality of ranges is distinctfrom each of the other ranges of bandwidths in the plurality of ranges.

Such a bandwidth control apparatus and method can be used to enablecontrol of laser light bandwidth at a narrower bandwidth (for example,in a range below 0.5 picometers (pm)) and at a wider bandwidth (forexample, in a range between 0.5 and 1.7 pm).

DRAWING DESCRIPTION

FIG. 1 is a block diagram of a light system providing input to anapparatus such as a lithography machine;

FIG. 2 is a block diagram of a bandwidth selection system of the lightsystem of FIG. 1;

FIG. 3 is a block diagram of an exemplary light source that can be usedin the light system of FIG. 1;

FIG. 4 is a block diagram of a control scheme used by a control systemof the light system of FIG. 1;

FIG. 5 is a block diagram of the control system used in the light systemof FIG. 1;

FIG. 6 is a flow chart of a procedure for selecting bandwidth in thelight system of FIG. 1;

FIG. 7 is a flow chart of a procedure for operating a first bandwidthactuation system of the light system of FIG. 1;

FIG. 8 is a flow chart of a procedure for switching from active controlof the first bandwidth actuation system to a second bandwidth actuationsystem of the light system of FIG. 1;

FIG. 9 is a flow chart of a procedure for operating the second bandwidthactuation system of the light system of FIG. 1;

FIG. 10 is a flow chart of a procedure for switching from active controlof the second bandwidth actuation system to the first bandwidthactuation system of the light system of FIG. 1; and

FIG. 11 is a flow chart of a procedure for operation of a firstbandwidth actuation system in a closed-loop transition mode.

DESCRIPTION

Referring to FIG. 1, a light system 100 includes a light source 102 thatproduces a light beam 104 that is delivered to an apparatus 106. Theapparatus 106 can include a lithography machine that includes a scannerthat requires several wavelengths centered on respective selectedwavelengths and having respective bandwidths. To this end, the lightsystem 100 also includes a bandwidth selection system (also referred toas a line narrowing module) 108 that receives a light beam 140 from thelight source 102 and finely tunes the spectral output of the lightsource 102, a beam analysis module 110 that measures one or moreproperties (including bandwidth information) of the light beam 104delivered to the apparatus 106, and a control system 112 connected tothe line narrowing module 108, the light source 102, the beam analysismodule 110, and the apparatus 106. Bandwidth information includes anyinformation that can be used to determine bandwidth. Therefore,bandwidth information can be the actual bandwidth or it can be ameasurement of another property from which the bandwidth can becalculated.

Among other purposes, as discussed below, the control system 112provides operation and control of the light source 102 at a plurality ofdistinct bandwidth ranges and enables the light source 102 toautomatically switch between the bandwidth ranges within a reasonableamount of time (for example, less than five seconds) without requiringmanual intervention to perform switching. In some implementations, abandwidth range is defined by an upper value of a bandwidth and a lowervalue of a bandwidth and all of the bandwidths between the upper valueand the lower value. A bandwidth range could also or alternatively bedefined by just an upper value or a lower value of a bandwidth and allof the bandwidths below (above) the upper (lower) value. A bandwidthrange is distinct from another bandwidth range if the upper values ofeach range are unequal and/or if the lower values of each range areunequal. Bandwidth ranges can be distinct yet still overlap even thoughthe upper and lower values are unequal. For example, a first bandwidthrange can be all bandwidth values below 0.5 pm (an upper range) and asecond bandwidth range can be values between 0.5 and 1.7 pm.

The control system 112 is able to effectuate the switching such thatonce the switching is complete, there is no discernable disturbance tonormal operation of the light source 102. The control system 112 is alsoconfigured to control certain other properties (for example, energyoutput, triggering times, timing, and dosage) of the light source 102.The control system 112 receives input from the beam analysis module 110,the apparatus 106, and components of the light source 102 to performthese operations. Additionally, the control system 112 can be connectedto an output device 116 such as a monitor, light, or audio device toprovide direct feedback to a user.

Referring also to FIG. 2, the line narrowing module 108 can include abandwidth control module 120 that includes electronics in the form ofany combination of firmware and software. The module 120 is connected totwo or more bandwidth actuation systems 122, 124, 126. Each of theactuation systems 122, 124, 126 can include one or more actuators thatare connected to respective optical features 132, 134, 136 of an opticalsystem 138. The bandwidth control module 120 receives a signal 114 fromthe control system 112, the signal 114 including specific commands tooperate or control one or more of the bandwidth actuation systems 122,124, 126.

Each optical feature 132, 134, 136 is optically coupled to the lightbeam 140 produced by the light source 102. The optical system 138 thatincludes the optical features 132, 134, 136 can include dispersiveoptical elements such as reflective gratings and refractive opticalelements such as rotatable prisms. An example of an optical system thatincludes optical features that are controlled by actuation systems canbe found in U.S. application Ser. No. 12/605,306, entitled “SystemMethod and Apparatus for Selecting and Controlling Light SourceBandwidth,” and filed on Oct. 23, 2009 (the '306 application), which isincorporated herein by reference in its entirety. In the '306application, an optical system is described that includes a beamexpander (including one or more prisms) and a dispersive element such asa grating.

Each of the actuators of the actuation systems 122, 124, 126 is amechanical device for moving or controlling the respective opticalfeatures 132, 134, 136 of the optical system 138. The actuators receiveenergy from the module 120, and convert that energy into some kind ofmotion imparted to the optical features 132, 134, 136 of the opticalsystem 138. For example, in the '306 application, actuation systems aredescribed such as force devices (to apply forces to regions of thegrating) and rotation stages for rotating one or more of the prisms ofthe bean expander. The actuation systems 122, 124, 126 can include, forexample, motors such as stepper motors, valves, pressure-controlleddevices, piezo-electric devices, linear motors, hydraulic actuators,voice coils, etc.

Based on inputs from the beam analysis module 110 and the apparatus 106,the line narrowing module 108 produces a light beam 150 (shown in FIG.2) that is narrowed to within a target bandwidth that is supplied to thecontrol system 112.

The beam analysis module 110 includes a bandwidth measurement system(also referred to as a bandwidth meter) 111 that includes at least onesensor that measures the bandwidth information of the light beam 104.The bandwidth measurement system 111 uses interferometric or dispersiveinstruments (such as spectrometers). For example, the bandwidthmeasurement system 111 can include one or more spectrometers havingdiffering impulse response functions such as what is described in U.S.Pat. No. 6,952,267, entitled “Method and Apparatus for MeasuringBandwidth of a Laser Output,” issued Oct. 4, 2005 (the '267 patent),which is incorporated herein by reference in its entirety. Eachspectrometer provides an output that is representative of a measuredparameter related to or containing information about the bandwidth ofthe light beam 104. The bandwidth measurement system 111 also includes acalculation apparatus that utilizes the spectrometer outputs as part ofa system of equations. The equations employ predetermined calibrationvariables specific to the spectrometer and are used to calculate anestimate of the bandwidth of the light beam 104 according to one or moremetrics. Such metric can be the spectrum full-width at some percentageor fraction (X) of the maximum value attained (FWXM), or it can be thewidth of a portion containing some percentage or fraction (Y) of thetotal energy (EY).

The bandwidth measurement system 111 includes a plurality of sets ofpredetermined calibration variables. Each of the plurality of sets isconfigured to provide a metric that is accurately tuned to estimatebandwidth over a particular range of wavelengths and at a particularcenter wavelength. For example, a first set of predetermined calibrationvariables can be associated with estimating bandwidth over a first rangeof bandwidths that is expected when operating the bandwidth actuationsystem 122 to actively control the optical feature 132. As anotherexample, a second set of predetermined calibration variables can beassociated with estimating a bandwidth over a second range of bandwidthsthat is expected when operating the actuation system 124 to activelycontrol the optical feature 134.

In some implementations, the light source 102 can be, for example, apulsed laser light source that produces as the light beam 104 a pulsedlaser beam. Referring also to FIG. 3, as an example of thisimplementation, the light source 102 includes a master oscillator (MO)300 that provides a seed laser beam 305 to a power amplifier (PA) 310.The control system 112 is coupled to the master oscillator 300 by way ofa connection 335 and to the power amplifier 310 by way of a connection340. The power amplifier 310 can be, for example, a regenerative ringresonator, as described in U.S. application Ser. No. 12/413,341,entitled “Regenerative Ring Resonator,” filed on Mar. 27, 2009, which isincorporated herein by reference in its entirety. The master oscillator300 enables fine tuning of parameters such as the center wavelength andthe bandwidth at relatively low output pulse energies. The poweramplifier 310 receives the seed laser beam 305 from the masteroscillator 300 and amplifies this output to attain the necessary powersin the light beam 104 (which is a laser beam in this implementation) foroutput to use in the apparatus 106.

The master oscillator 300 includes a discharge chamber having twoelongated electrodes, a laser gas, and a fan for circulating the gasbetween the electrodes, and a laser resonator is formed between the linenarrowing module 108 on one side of the discharge chamber and an outputcoupler 315 on a second side of the discharge chamber. The masteroscillator 300 can also include a line center analysis module 320 thatreceives an output from the output coupler 315 and one or more beammodification optical systems 325 that modify the size and/or shape ofthe laser beam as needed. The laser gas used in the discharge chambercan be any suitable gas for producing a laser beam at a requiredwavelength and bandwidth, for example, the laser gas can be argonfluoride (ArF), which emits light at a wavelength of about 193 nm, orkrypton fluoride (KrF), which emits light at a wavelength of about 248nm.

The power amplifier 310 includes a power amplifier discharge chamber,and if it is a regenerative ring amplifier, the power amplifier 310 alsoincludes a beam reflector 330 that reflects the laser beam back into thedischarge chamber to form a circulating path. The power amplifierdischarge chamber includes a pair of elongated electrodes, a laser gas,and a fan for circulating the gas between the electrodes. The seed laserbeam 305 is amplified by repeatedly passing through the power amplifier310. The beam modification optical system 325 provides a way (forexample, a partially-reflecting mirror) to in-couple the seed laser beam305 and to out-couple a portion of the amplified radiation from thepower amplifier 310 to form the output laser beam 104.

Referring again to FIG. 1, the output laser beam 104 from the lightsource 102 can additionally be directed through a beam modificationsystem 160 that can include one or more of a pulse stretcher, an autoshutter, and a beam delivery unit. At the pulse stretcher, each of thepulses of the output laser beam 104 can be stretched, for example, in anoptical delay unit, to adjust for performance properties such as dose orexposure of the laser beam that impinges the apparatus 106. The laserbeam 104 that exits the pulse stretcher can then be directed through theauto shutter before entering the beam delivery unit that directs thelaser beam 104 to the apparatus 106.

Referring to FIGS. 4 and 5, the control system 112 operates using anerror signal 400 obtained from an absolute value of a difference 405between target bandwidth information 410 and measured bandwidthinformation 415. The measured bandwidth information 415 can bedetermined directly from an output 425 of the bandwidth measurementsystem 111 or it can be determined by removing noise 420 from the output425 of the bandwidth measurement system 111. The output 114 from thecontrol system 112 is sent to the line narrowing module 108(specifically to the bandwidth control module 120, which outputs signalsthe actuation systems 122, 124, 126), which is connected to the lightsource 102 to cause changes in operation of the light source 102 tothereby change a bandwidth 435 output from the light source 102. Thebandwidth measurement system 111 receives a portion of the light beam104 for analysis of bandwidth, the light beam portion having a bandwidth430 that is a combination of the bandwidth 435 controlled by one or moreof the bandwidth actuation systems 122, 124, 126 and a disturbance 440to the bandwidth 435, the disturbance 440 being caused by propertiesthat vary within the light source such as, for example, thermal effectswithin the gas in the chambers or of the optical components within thelight source 102, changes in output energy of the light source 102,changes in alignment or positioning of components within the lightsource 102, and acoustic effects (that can be observed through theeffects of changes in a repetition rate of pulses of the light beam104).

The control system 112 includes sub-systems (for example, sub-programs)such as a target bandwidth switch 500 (FIG. 5) that can select a targetrange of bandwidths from among a plurality of target ranges based on thetarget bandwidth information 410 supplied from a user or from theapparatus 106. Other sub-systems of the control system 112 include a setof operation modes associated with each of the target ranges. Thecontrol system 112 uses one or more of proportional, integral, andderivative control values in each of the modes. For a first target rangeof bandwidths 505, the control system 112 operates in a first rangenormal mode 510, which is considered a steady-state mode, aftercompleting a first range switching mode 535, which is considered atemporary mode that enables the transition to the first range normalmode 510. For example, the first range normal mode 510 can be aclosed-loop control mode that uses one or more of proportional,integral, and derivative control values. In the first range normal mode510, the first bandwidth actuation system 122 is operated. The firstrange switching mode 535 can be an open-loop control mode or aclosed-loop control mode.

Operation of the control system 112 in the first range normal mode 510can be similar to the operation described in U.S. Pat. No. 6,393,037,entitled “Wavelength Selector for Laser with Adjustable AngularDispersion,” issued on May 21, 2002 (the '037 patent) and the operationdescribed in U.S. Publication No. 2008/0253413, entitled “LaserLithography System with Improved Bandwidth Control,” filed on Apr. 9,2008 (the '413 publication), both of which are incorporated herein byreference in their entirety. In these references, a magnification of abeam is changed prior to incidence on a dispersive element, and as themagnification is changed, the bandwidth of the light reflected from thedispersive element is changed. The magnification of the beam can bechanged by actively introducing a change in an orientation (for example,an angle) of a beam expander (one or more prisms of a set of prisms).Thus, in the first range normal mode 510, the control system 112 can beconfigured to control the bandwidth actuation system 122 to modify anorientation (for example, an angle) of the optical feature (a beamexpander) 132 to vary the magnitude of the angular dispersion providedby a dispersive element (a grating) in the optical system 138 to selecta bandwidth in the first range of bandwidths.

For a second target range of bandwidths 515, the control system 112operates in a second range normal mode 525 (considered a steady-statemode) after completing a second range switching mode 520, which is atemporary mode that enables the transition to the second range normalmode 525. For example, the second range normal mode 525 can be a closedloop control mode that uses integral control with a low gain while thesecond range switching mode 520 can be a closed loop control mode thatuses proportional-integral control with a high gain. A “low” gain isgenerally one that yields very robustly stable (so-called“over-damped”), but somewhat slow (relative to actuator speed)closed-loop performance. A “high” gain is one that yields under-damped(oscillatory) performance, but is faster than low gain relative to theactuator speed. Each of these modes is described in greater detail belowwith reference to FIGS. 6-10.

For simplicity, the control system 112 shown in FIG. 5 and describedbelow includes two target ranges of bandwidth and operates between thesetwo target ranges. However, the control system 112 can include three ormore target ranges and the procedure performed by the control system 112can be modified to extend to three or more target ranges. For three ormore ranges, the target bandwidth switch 500 switches between thesethree or more target ranges and the control system 112 includes othermodes corresponding to operation in and switching between the othertarget ranges, as needed.

Referring also to FIG. 6, the control system 112 performs a procedure600 for operating and controlling the light source 102 includingcontrolling a bandwidth of the light beam 104 output to the apparatus106.

The control system 112 performs parallel processes, two of which areshown in FIG. 6. In a first process (shown in the left hand side of thedrawing as a generalized process), the control system 112 turns on thelight source 102 (step 602) and outputs commands to the light source 102to produce a light beam (step 604). For example, if the light source 102is the laser source shown in FIG. 3 that includes a master oscillator300 and a power amplifier 310, then the control system 112 (through theconnections 335 and 340) controls the pulse energy and accumulated doseenergy output from the laser source at predetermined pulse repetitionrates. In this case, the control system 112 also provides triggering ofthe discharges in the chamber of the master oscillator and thedischarges in the chamber of the power amplifier relative to each otherwith feedback and feed-forward control of the pulse and dose energy. Thecontrol system 112 determines if a request (for example, from theapparatus 106) is received to shut off the light source 102 (step 606)and if so, the control system 112 turns off the light source 102 (step608).

The control system 112 also performs a second process (shown in theright hand side of the drawing) for controlling bandwidth of the lightbeam 104 while the control system 112 outputs commands to the lightsource 102 (step 604). In this second process, the control system 112operates a first bandwidth actuation system (such as, for example, thebandwidth actuation system 122) in the first range normal mode 510 (step610). The control system 112 determines if a request, for example, fromthe apparatus 106 or from a user, has been received to change thebandwidth of the light beam 104 from the first bandwidth range to asecond bandwidth range that is distinct from the first bandwidth range(step 615). If the request has not been received (step 615), then thecontrol system 112 continues to operate the first bandwidth actuationsystem 122 in the first range normal mode 510 (step 610). If, on theother hand, the request has been received (step 615), then the controlsystem 112 switches from active control of the first bandwidth actuationsystem to active control of a second bandwidth actuation system (suchas, for example, the bandwidth actuation system 124) in the second rangeswitching mode 520 (step 620).

After switching is completed (step 620), the control system 112 operatesthe second bandwidth actuation system in the second range normal mode525 (step 625). The control system 112 determines if a request, forexample, from the apparatus 106 or from a user, has been received tochange the bandwidth of the light beam 104 from the second bandwidthrange to the first bandwidth range (step 630). If the control system 112determines that request has not been received (step 630), then thecontrol system 112 continues to operate the second bandwidth actuationsystem in the second range normal mode 525 (step 625). If the controlsystem 112 determines that the request has been received (step 630),then the control system 112 switches from active control of the secondbandwidth actuation system to active control of the first bandwidthactuation system in the first range switching mode 535 (step 635). Uponcompletion of switching, the control system 112 returns to operating thefirst bandwidth actuation system in the first range normal mode 510(step 610).

Referring to FIG. 7, the control system 112 performs an exemplaryprocedure 610 for operating the first bandwidth actuation system (suchas, for example, the bandwidth actuation system 122) in the first rangenormal mode 510. During the procedure 610, the control system 112receives measured bandwidth information 415 from the bandwidthmeasurement system 111 (step 700). In this case, because the controlsystem 112 is operating in the first range normal mode 510, thebandwidth measurement system 111 is using a first set of predeterminedcalibration variables to estimate the bandwidth information of theportion of the light beam 104. For example, the bandwidth measurementsystem 111 can use a metric such as the EY metric (which is the width ofa portion containing some percentage or fraction “Y” (for example, 95%)of the total energy) to estimate the bandwidth of the light beam 104.The control system 112 determines if the measured bandwidth information415 matches the target bandwidth information 410 (step 705).

The measured bandwidth information 415 can match the target bandwidthinformation 410 using any suitable test as there are several differentways to determine such matching. For example, the match determinationcould compare a weighted sum of the last N readings of bandwidth error(from target) against a threshold value. The bandwidth error is theabsolute difference between the measured bandwidth and the targetbandwidth. As another example, the match determination could simplydetect when the sign of an arithmetic difference between (a possiblyfiltered) measured bandwidth and a target bandwidth changes.

The control system 112 can estimate a bandwidth by combining (noisy)measurements (from the measured bandwidth information 415) with aprediction (using a math model) based on the current actuator commandsin a technique that can be referred to as “optimal estimation.” In thiscase, the control system 112 determines if the measured bandwidthinformation 415 matches the target bandwidth information 410 bydetermining if this optimal estimation is different from a targetbandwidth.

In another example, the matching determination can include determiningif the bandwidth error is within a threshold for a certain amount ofconsecutive time. In yet another example, the matching determination caninclude determining whether the rate of change of the bandwidth errorchanges sign at least N times (this can be thought of as error signaloscillation with N oscillations). Moreover, most of these matchingdeterminations are independent, so that one or more of the variouspossible independent matching determinations can be combined todetermine whether the measured bandwidth information 415 matches thetarget bandwidth information 410 (step 705).

In some implementations, the measured bandwidth information 415 matchesthe target bandwidth information 410 if the absolute value of thedifference 400 between the measured bandwidth information 415 and thetarget bandwidth information 410 is below a predetermined thresholdvalue. If the measured bandwidth information 415 matches the targetbandwidth information 410, then the control system 112 maintains thefirst bandwidth actuation system 122 in its current state (step 710). Ifthe measured bandwidth information 415 does not match the targetbandwidth information 410, then the control system 112 adjusts the firstbandwidth actuation system 122 in a direction that causes the opticalfeature 132 to move to a new position to select new bandwidthinformation (such as a new bandwidth) that is closer to the targetbandwidth information (for example, a target bandwidth) (step 715).

In some implementations, in the first range normal mode 510, the controlsystem 112 uses an adjustment of a magnification of a beam incident on adispersive element in the line narrowing module 108 to maintain themeasured bandwidth information 415 near the target bandwidth information410.

Referring to FIG. 8, the control system 112 performs a procedure 620 toswitch from active control of the first bandwidth actuation system (suchas, for example, the bandwidth actuation system 122) to active controlof the second bandwidth actuation system (such as, for example, thebandwidth actuation system 124) in the second range switching mode 520.The control system 112 stores information about the current state of thefirst bandwidth actuation system 122 (step 800). For example, thecontrol system 112 stores information about the current state of theoptical feature 132 (for example, the angle of the beam expander or themagnitude of the angular dispersion of the dispersive element) withinthe optical system 138. The control system 112 also provides anotification that it is in the second range switching mode 520 byoutputting this notification as a signal to the output device 116 (step805).

The control system 112 then sets the first bandwidth actuation system122 to a previously-calibrated and fixed state (step 810). For example,each of the actuators within the first bandwidth actuation system 122 isset to a respective fixed state. The fixed state can be pre-determinedusing a suitable measurement method. For example, the fixed state can bethe state of the first bandwidth actuation system at the moment therequest to change the bandwidth of the produced light beam from thefirst bandwidth range to the second bandwidth range is received. Asanother example, the fixed state can be determined from a function ofthe state of the first bandwidth actuation system at the moment that arequest is received to change the bandwidth of the produced light beamfrom the first bandwidth range to the second bandwidth range.

Even though the first bandwidth actuation system 122 is in the fixedstate, it is possible for the first bandwidth actuation system 122 toimpact the bandwidth of light beam 104. Therefore, two or more bandwidthactuation systems can influence the bandwidth of the light beam 104 atany one moment, but only one bandwidth actuation system is activelycontrolled at any one moment. The actual bandwidth of the light beam 104is, at all times, a function of all of the actuator states even thoughonly one of the bandwidth actuation systems is used to control thebandwidth within its particular range of bandwidths at any oneparticular moment. For example, the control system 112 actively controlsthe second bandwidth actuation system at step 625 but during this time,the control system 112 also maintains the first bandwidth actuationsystem in the fixed state and the bandwidth of the light beam 104depends on both of the bandwidth actuation system states. For example,the second bandwidth actuation system can be used for controlling andselecting a “coarse” bandwidth range, while the first bandwidthactuation system can be used for controlling and selecting a bandwidthin a “fine” manner.

The control system 112 also sends a signal to the bandwidth measurementsystem 111 to switch from a first configuration that uses the first setof predetermined calibration variables that are more tuned tomeasurements within the first bandwidth range to a second configurationthat uses the second set of predetermined calibration variables that aremore tuned to measurements within the second bandwidth range (step 815).

The control system 112 operates the second bandwidth actuation system124 in a transition mode (step 820). In this mode, the control system112 receives measured bandwidth information 415 (for example, a measuredbandwidth) from the bandwidth measurement system 111 (step 821) anddetermines if the measured bandwidth information 415 matches the targetbandwidth information 410 (step 822). As discussed above with respect tostep 705, the control system 112 can use any suitable method todetermine matching. In some implementations, the control system 112makes the matching determination using a combination of noise filteringand threshold logic, as described above in FIG. 4. Thus, for example,noise 420 is filtered from the measured bandwidth information 415 beforebeing received by the control system 112. Moreover, the control system112 can employ basic threshold logic in making this determination. Thus,the control system 112 can determine if the error signal 400 (that is,the absolute difference between the measured bandwidth information 415and the target bandwidth information 410) is below a predeterminedthreshold value.

If the control system 112 determines that there is no match (step 822),then the control system 112 adjusts the second bandwidth actuationsystem 124 in a direction that causes the optical feature 134 to move toa new position to select new bandwidth information (such as a newbandwidth) that is closer to the target bandwidth information 410 (forexample, a target bandwidth) (step 830). During this step, the firstbandwidth actuation system 122 (and other bandwidth actuation systemsexcluding the bandwidth actuation system 124) is in the fixed state.Moreover, the gain of the feedback provided to the control system 112 isvery high during the transition mode (step 820) to enable a more rapidcompletion of the transition to operating the second bandwidth actuationsystem 124 in the second range normal mode 525.

If the control system 112 determines that there is a match (step 822),then the control system 112 operates in a relatively brief reset mode inwhich it initiates a series of reset functions to allow it to learn andset other system states to a new operational condition (step 825). Thereset mode is included because adjustments of bandwidth actuators cancause other laser parameters (for example, energy, laser gain, etc.) tochange enough that their control systems do not function at anacceptable level. The reset mode essentially allows time for these othercontrol systems to “learn” and adapt to the new laser parameters. Ingeneral, a reset may be necessary on any switch from any bandwidth rangeto any other bandwidth range. Moreover, each type of transition may haveits own unique reset function. After the control system 112 determinesthat the reset mode is complete (step 830), the control system 112 thenoperates the second bandwidth actuation system in the second rangenormal mode 525 (step 625).

Referring to FIG. 9, the control system 112 performs an exemplaryprocedure 625 for operating the second bandwidth actuation system (suchas, for example, the bandwidth actuation system 124) in the second rangenormal mode 525. During the procedure 625, the control system 112receives measured bandwidth information 415 from the bandwidthmeasurement system 111 (step 900). In this case, because the controlsystem 112 is operating in the second range normal mode 525, thebandwidth measurement system 111 is using a second set of predeterminedcalibration variables to estimate the bandwidth information of theportion of the light beam 104. For example, the bandwidth measurementsystem 111 can use a metric such as the EX metric (which is the width ofa portion containing some percentage or fraction (for example, 95%) ofthe total energy) to estimate the bandwidth of the light beam 104. Thecontrol system 112 determines if the measured bandwidth information 415matches the target bandwidth information 410 (step 905). As discussedabove with respect to step 705, the control system 112 can use anysuitable method to determine matching. In some implementations, themeasured bandwidth information 415 matches the target bandwidthinformation 410 if the absolute value of the difference 400 between themeasured bandwidth information 415 and the target bandwidth information410 is below a predetermined threshold value. If the measured bandwidthinformation 415 matches the target bandwidth information 410 (step 905),then the control system 112 maintains the second bandwidth actuationsystem 124 in its current state (step 910). If the measured bandwidthinformation 415 does not match the target bandwidth information 410,then the control system 112 adjusts the second bandwidth actuationsystem 124 in a direction that causes the optical feature 134 to move toa new position to select new bandwidth information (such as a newbandwidth) that is closer to the target bandwidth information (forexample, a target bandwidth) (step 915).

In some implementations, the optical feature 134 is a dispersive opticalbody such as a grating and in the second range normal mode 525, thecontrol system 112 adjusts one or more forces applied to the grating inthe line narrowing module 108 to maintain the measured bandwidthinformation 415 near the target bandwidth information 410. Such a secondrange normal mode 525 is described in the '306 application, discussedabove. Additionally, in the second range normal mode 525, the firstoptical feature 132 is maintained at a fixed state since the firstbandwidth actuation system 122 is maintained at its fixed state (step810).

In some implementations, the control system 112 can perform activecontrol (steps 905-915) of the second bandwidth actuation system 124only under certain operating conditions of the light source 102, forexample, if the repetition rate of the light source 102 is maintainedwithin a predetermined suitable range. Thus, if the light source 102fires outside the predetermined suitable range, then the control system112 maintains the second bandwidth actuation system 124 at its currentstate, effectively operating in an open loop mode.

Referring to FIG. 10, the control system 112 performs a procedure 635 toswitch from active control of the second bandwidth actuation system(such as, for example, the bandwidth actuation system 124) to activecontrol of the first bandwidth actuation system (such as, for example,the bandwidth actuation system 122) in the first range switching mode535. The control system 112 operates the first bandwidth actuationsystem 122 in a transition mode (step 1000). In some implementations, inthe transition mode (step 1000), the first bandwidth actuation system122 is commanded to the state that was stored in step 800.

The control system 112 then sets the second bandwidth actuation system124 to a fixed state (step 1005). For example, each of the actuatorswithin the second bandwidth actuation system 124 is set to a respectivefixed state. In some implementations, the fixed state can be the stateof the second bandwidth actuation system at the moment the request tochange the bandwidth of the produced light beam from the secondbandwidth range to the first bandwidth range is received. In otherimplementations, the fixed state is a pre-determined state that isdetermined during calibration.

The control system 112 sends a signal to the bandwidth measurementsystem 111 to switch from the second configuration that uses the secondset of predetermined calibration variables that are more tuned tomeasurements within the second bandwidth range to the firstconfiguration that uses the first set of predetermined calibrationvariables that are more tuned to measurements within the first bandwidthrange (step 1010). The control system 112 also provides a notificationthat it is in the first range switching mode 535 by outputting thisnotification as a signal to the output device 116 (step 1015).

Next, the control system 112 operates in a relatively brief reset modein which it initiates a series of reset functions to allow it to learnand set other system states to a new operational condition (step 1020).After the control system 112 determines that the reset mode is complete(step 1025), the control system 112 then operates the first bandwidthactuation system in the first range normal mode 510 (step 610).

Referring also to FIG. 11, in some implementations, the transition modeat step 1000 can be a closed-loop control mode in which the controlsystem 112 receives measured bandwidth information 415 (for example, themeasured bandwidth) from the bandwidth measurement system 111 (step1021) and determines if the measured bandwidth information 415 matchesthe target bandwidth information 410 (step 1022). As discussed abovewith respect to step 705, the control system 112 can use any suitablemethod to determine matching. For example, the control system 112 makesthe determination using a combination of noise filtering and thresholdlogic, as described above in FIG. 4. If the control system 112determines that there is no match (step 1022), then the control system112 adjusts the first bandwidth actuation system 122 in a direction thatcauses the optical feature 132 to move to a new position to select newbandwidth information (such as a new bandwidth) that is closer to thetarget bandwidth information 410 (for example, a target bandwidth) (step1023). During this step, the second bandwidth actuation system 124 (andany bandwidth actuation system other than the first bandwidth actuationsystem 122) is maintained in its respective fixed state. If the controlsystem 112 determines that there is a match (step 1022), then thecontrol system 112 operates in the brief reset mode (step 1025).

As discussed above, the light system 100 can be a laser system thatoperates on a lithography machine 106. In this case, the laser system100 is able to operate and control the laser source 102 at two or moredistinct bandwidths. For example, in this implementation, the firstdistinct bandwidth range can be a narrower bandwidth range, for example,less than about 0.5 pm and the second distinct bandwidth range can be awider bandwidth range, for example, between about 0.5 and about 1.7 pm.Such a wider bandwidth range can be useful in applications such as focusdrilling, which enables certain lithographic processes (such as creatingcontact holes) to be more efficiently and suitably performed.

In some implementations, the metric that can be used to measure thebandwidth of the light beam 104 can be mean absolute defocus (MAD),which is described in U.S. Application No. 61/236,848, “Active SpectralControl of Laser Light Source,” filed on Aug. 25, 2009, which isincorporated herein by reference in its entirety.

The control system 112 can include one or more of digital electroniccircuitry, computer hardware, firmware, and software. The control system112 can also include appropriate input and output devices, a computerprocessor, and a computer program product tangibly embodied in amachine-readable storage device for execution by a programmableprocessor. The procedure embodying the techniques (discussed above) maybe performed by a programmable processor executing a program ofinstructions to perform desired functions by operating on input data andgenerating appropriate output. Generally, a processor receivesinstructions and data from a read-only memory and/or a random accessmemory. Storage devices suitable for tangibly embodying computer programinstructions and data include all forms of non-volatile memory,including, by way of example, semiconductor memory devices, such asEPROM, EEPROM, and flash memory devices; magnetic disks such as internalhard disks and removable disks; magneto-optical disks; and CD-ROM disks.Any of the foregoing may be supplemented by, or incorporated in,specially-designed ASICs (application-specific integrated circuits).

Other implementations are within the scope of the following claims.

What is claimed is:
 1. A method comprising: producing a light beam;controlling a bandwidth of the produced light beam within a first targetrange of bandwidths including activating and controlling a firstbandwidth actuation system connected to a first optical featureoptically coupled to the produced light beam; controlling a bandwidth ofthe produced light beam within a second target range of bandwidthsincluding activating and controlling a second bandwidth actuation systemconnected to a second optical feature optically coupled to the producedlight beam; and switching between activating and controlling the firstbandwidth actuation system and activating and controlling the secondbandwidth actuation system independently and separately of activatingand controlling the first bandwidth actuation system based on a providedbandwidth measurement and a selected target bandwidth; wherein: thesecond target range of bandwidths is distinct from the first targetrange of bandwidths, only the first bandwidth actuation system is usedto control the bandwidth of the produced light beam within the firsttarget range of bandwidths, and only the second bandwidth actuationsystem is used to control the bandwidth of the produced light beamwithin the second target range of bandwidths.
 2. The method of claim 1,further comprising receiving a request to change a bandwidth of theproduced light beam from the first target range of bandwidths to thesecond target range of bandwidths.
 3. The method of claim 1, furthercomprising switching between bandwidth control within the first targetrange and bandwidth control within the second target range in responseto a command to switch.
 4. The method of claim 1, further comprisingswitching between bandwidth control within the first target range tobandwidth control within the second target range, wherein the switchingincludes: selecting second target bandwidth information; setting thefirst bandwidth actuation system to a first fixed state; switching abandwidth measurement system from a first configuration to a secondconfiguration; receiving measured bandwidth information from thebandwidth measurement system; determining whether the measured bandwidthinformation matches the second target bandwidth information; andactivating the second bandwidth actuation system to cause the secondoptical feature to modify the bandwidth of the produced light beam untilit is determined that the measured bandwidth information matches thesecond target bandwidth information.
 5. The method of claim 4, whereinreceiving measured bandwidth information from the bandwidth measurementsystem includes receiving the measured bandwidth information whileoperating in the second configuration.
 6. The method of claim 4, furthercomprising storing information about the state of one or more componentsof the first bandwidth actuation system before setting the firstbandwidth actuation system to the first fixed state.
 7. The method ofclaim 4, wherein the first fixed state is the state of the firstbandwidth actuation system at the moment the request to change thebandwidth of the produced light beam from the first target bandwidthrange to the second target bandwidth range is received.
 8. The method ofclaim 4, wherein the first fixed state is determined from a function ofthe state of the first bandwidth actuation system at the moment that arequest is received to change the bandwidth of the produced light beamfrom the first target bandwidth range to the second target bandwidthrange.
 9. The method of claim 4, further comprising controlling thesecond bandwidth actuation system to reduce an absolute error betweenthe measured bandwidth information and the second target bandwidthinformation until a request is received to change the bandwidth of theproduced light beam from the second target bandwidth range to the firsttarget bandwidth range.
 10. The method of claim 4, further comprisingcontrolling the second bandwidth actuation system in a reset mode afterswitching the bandwidth measurement system from the first configurationto the second configuration.
 11. The method of claim 4, furthercomprising switching between bandwidth control within the second targetrange to bandwidth control within the first target range upon receipt ofthe request to change bandwidth of the produced light beam from thesecond target bandwidth range to the first target bandwidth range,switching including: selecting first target bandwidth information;setting the second bandwidth actuation system to a second fixed state;switching the bandwidth measurement system from the second configurationto the first configuration; receiving measured bandwidth informationfrom the bandwidth measurement system while operating in the firstconfiguration; determining whether the measured bandwidth informationmatches the first target bandwidth information; and activating the firstbandwidth actuation system to cause the first optical feature to modifythe bandwidth of the produced light beam until it is determined that themeasured bandwidth information matches the first target bandwidthinformation.
 12. The method of claim 11, wherein the second fixed stateis the state of the second bandwidth actuation system at the moment therequest to change the bandwidth of the produced light beam from thesecond target bandwidth range to the first target bandwidth range isreceived.
 13. The method of claim 11, wherein the second fixed state isa pre-determined state that is determined during calibration.
 14. Themethod of claim 11, further comprising controlling the first bandwidthactuation system to reduce the absolute error between the measuredbandwidth information and the first target bandwidth information until arequest is received to change the bandwidth of the produced light beamfrom the first target bandwidth range to the second target bandwidthrange.
 15. The method of claim 11, further comprising sending a signalto the first bandwidth actuation system to return to the state that wasstored prior to setting the first bandwidth actuation system to thefirst fixed state.
 16. The method of claim 11, further comprisingcontrolling the first bandwidth actuation system in a reset mode afterswitching the bandwidth measurement system from the second configurationto the first configuration.
 17. The method of claim 1, furthercomprising switching between bandwidth control within the first targetrange to bandwidth control within the second target range, whereinswitching between bandwidth control within the first target range tobandwidth control within the second target range comprises switching abandwidth measurement system from a first configuration to a secondconfiguration.
 18. The method of claim 17, wherein switching thebandwidth measurement system from the first configuration to the secondconfiguration includes switching from a first set of calibrationvariables to a second set of calibration variables.
 19. The method ofclaim 18, wherein: the first set of calibration variables ispredetermined and configured to provide a metric that is tuned toestimate bandwidth over the first target range of bandwidths; and thesecond set of calibration variables is predetermined and configured toprovide a metric that is tuned to estimate bandwidth over the secondtarget range of bandwidths.
 20. The method of claim 1, wherein producingthe light beam includes producing a laser beam.
 21. A method ofcontrolling a bandwidth of a pulsed laser beam comprising: producing thepulsed laser beam; receiving measured bandwidth information of theproduced laser beam from a bandwidth measurement system; based on thereceived measured bandwidth information, controlling a bandwidth of theproduced laser beam to within a plurality of target ranges ofbandwidths; for each of the target ranges of bandwidths, activating andcontrolling a bandwidth actuation system connected to an optical featureoptically coupled to the produced laser beam; and switching betweencontrolling one of the bandwidth actuation systems and controllinganother of the bandwidth actuation systems independently and separatelyof controlling one of the bandwidth actuation systems based on thereceived measured bandwidth information and a selected target bandwidth;wherein: each target range of bandwidths in the plurality of targetranges is distinct from each of the other target ranges of bandwidths inthe plurality of ranges, and only one of the bandwidth actuation systemsis activated and controlled to control the bandwidth to within aparticular target range of bandwidths at any one particular moment. 22.The method of claim 21, further comprising receiving a request to changea bandwidth of the produced light beam from one of the target range ofbandwidths to another of the target range of bandwidths.
 23. The methodof claim 21, further comprising switching between bandwidth controlwithin a first target range of bandwidths by controlling a firstbandwidth actuation system and bandwidth control within a second targetrange of bandwidths by controlling a second bandwidth actuation systemin response to a command to switch.
 24. The method of claim 23, whereinthe switching includes: selecting second target bandwidth information;setting the first bandwidth actuation system to a first fixed state;switching a bandwidth measurement system from a first configuration to asecond configuration; determining whether the measured bandwidthinformation matches the second target bandwidth information; andactivating the second bandwidth actuation system to cause the secondoptical feature to modify the bandwidth of the produced light beam untilit is determined that the measured bandwidth information matches thesecond target bandwidth information.